In electroslag remelting processes, material electrodes are remolten in order to produce material ingots, wherein the latter are used as semifinished products for the manufacture of components with high material quality such as, for example, forgings for use in power plants that have to meet the strictest reliability requirements. With respect to the systems or methods used, one distinguishes between two systems, the first of which is the so-called sliding crucible or ingot retraction system, in which the crucible apparatus, in which the ingots produced by melting the electrodes solidify, is provided with a crucible bottom that can be displaced independently of or together with a crucible wall in order to effectively manufacture the ingots in the form of a continuous slab. In so-called stationary crucible systems, the material electrodes are remolten into an ingot that is defined with respect to its linear dimension, wherein the crucible apparatus used in this case features a fixed crucible bottom.
In order to control the course of the cooling process that is essential for the material quality of the ingot, particularly in the region of the ingot base formed by the lower end of the ingot, it is known to realize the crucible bottom of crucible apparatuses used in stationary crucible systems in a heatable fashion. In this case, a bottom plate of the crucible bottom that is in contact with the ingot is indirectly tempered. A heat transfer medium such as, for example, water or oil is used for the tempering process. Consequently, the ingot mass in the crucible is tempered indirectly because the heat transfer medium initially needs to be heated to the desired temperature by means of a suitable energy carrier before a heat transfer to the ingot base can be realized via the bottom plate of the crucible bottom. The known heating method therefore is relatively sluggish such that it is hardly possible, in particular, to achieve desired temperature profiles during the heating of the ingot base. In addition, shrinkage of the ingot base occurs, in particular, in the region of the ingot base surface such that the ingot base frequently is not in direct contact with the bottom plate over its entire surface area.
A particular problem also arises due to the fact that the bottom plate consists of copper or a copper alloy in order to realize an adequate heat transfer such that the temperature of the bottom plate is limited to about 200° C. due to its material. It therefore must be assumed that the conventional ingot base heating process merely makes it possible to achieve slight temperature gradients on the one hand and also a relatively small temperature increase of the ingot base on the other hand.